1) The information regarding DNA size and conformation inherent in the rate of change of electrophoretic mobility with gel concentration (Ferguson plot) was derived from pore gradient gels oriented at a right angle to the direction of polymerization (transverse pore gradient gels). This approach avoids the previous assumption of the proportionality between size and migration distance, overcomes limitations in the number of bands and is non-laborious. 2) Agarose gel electrophoresis in discontinuous buffer systems is operative at low DNA load (1 microgram/squ.cm) and at 0.04 M ionic strength. These conditions avoid previous perturbed gel patterns. 3) Free mobility of proteins was measured by polyacrylamide gel electrophoresis in the presence of 0.4% agarose, exploiting the absence of significant sieving effects at this concentration. This allows one to identify a molecule by size and charge, to pinpoint the optimal way of separating it from the species migrating as neighboring bands and to computer simulate migration. 4) Apparatus for electrophoresis with continuous monitoring through epifluorescence microscopy was constructed. It allows one to visualize, and take measurements on, single DNA molecules up to several hundred kb in size during electrophoresis. 5) Apparatus for electrophoresis in sieving media consisting of liquid polymer solutions was constructed. Size separation of polystyrene particles in the range of 125 to 1,000 nm radius was achieved. Mobilities in that size range were found to be proportional to particle size. 6) Continuous optical scanning of gels during electrophoresis was compared with conventional detection of gel patterns at a single point of observation. This comparison aims at finding the minimal throughput time and the maximal number of components separable per unit length of gel, and at validating, or invalidating, the assumed advantages of continuous pattern observation. 7) Glutaraldehyde crosslinked polyvinylalcohol with molecular weights of 25,000 and 650,000 was evaluated as a gel electrophoretic medium. 8) Exportable programs for analysis of gels on the basis of the extended Ogston model at single concentration, 2-D agarose gels (ELPHOFIT) and linear pore gradients (GRADFIT) were written.